1. Field of the Invention
The present invention relates to a measurement data generation apparatus for measuring, by sampling, object movement which nonlinearly changes over time.
2. Discussion of the Background
When sampling/measurement of an engine rpm, cylinder temperature, pressure and the like which indicate operating conditions of a vehicle is performed, a clock signal generated by a reference signal oscillator independent1y arranged in the measuring apparatus is used as a sampling signal. Analog data obtained by sampling is converted into digital data and is supplied to a microcomputer mounted on the vehicle. The engine operation is controlled in accordance with such digital data.
In this case, the period of the clock signals generated by the reference clock generator remains constant. However, when the engine rotates irregularly, the number of samples obtained upon one revolution of the engine differs from that obtained upon another revolution of the engine. This prevents correct measurement of the operating conditions of the engine and reliable control of the engine.
When cylinder pressure of a reciprocal engine at a position which is before the top dead center by 30.degree. is being measured, the conventional measurement apparatus can not produce a sampling pulse correctly at the position where the engine is before the top dead center by 30.degree.. To this end, a plurality of data is obtained for the position near the desired position before the top dead center by 30.degree.. The obtained data is then statistically processed to have an approximated measurement value at the desired position. This conventional measurement method, however, requires much time. Moreover, since the engine operation state varies with time, it is not possible to obtain a correct data. Particularly, even if an irregular or remarkable phenomenon occurs once for several revolutions of the engine, a data representing such a phenomenon can not be obtained, because the measurement data is processed statistically to have an average data. When the temperature variation in an engine is being measured for 24 hours from the start of the engine, it is necessary to set the sampling frequency high for the initial operation period at which the temperature variation rate is relatively high. If this is the case, however, number of sampled data obtained after the engine temperature reaches to a normal running state also becomes very large, thereby requiring much labor and consuming time.
Further, it is difficult to correctly reproduce a characteristic curve representing a relationship between a rotational position of an engine and the pressure in a cylinder, because a correct relationship between the rotational position and the pressure can not be obtained by the conventional measurement method. For the precise approximation of the reproduced characteristic curve with the original curve, it is necessary to statistically process many samples. This method, however, requires much time and fails the correct reproduction of the original curve.